A photocoupler is a semiconductor device, which transmits a signal via optical coupling between a light-emitting element and a light-receiving element that are built in a package. A primary side lead connected to the light-emitting element and a secondary side lead connected to the light-receiving element are electrically insulated so that, for example, a low-voltage circuit connected to the primary side can control a high-voltage circuit on the secondary side.
The photocoupler used in such manner may employ, as the light-receiving element, a thyristor that is turned on by photocurrent, for example. The thyristor generally has a vertical structure in which current flows from an electrode on a front face side to an electrode on a back face side, and satisfies a peak forward blocking voltage of 400 V to 600 V required for the design, for example. However, a process of manufacturing the thyristor having the vertical structure includes a lengthy impurity diffusion process, requiring a long turnaround time to be completed. As a result, the whole process of manufacturing the photocoupler including the process of manufacturing the thyristor would have a long lead time, resulting in a low manufacturing efficiency. Thus, there is required a photocoupler using a thyristor in a lateral structure that has a shorter time of the manufacturing process.